# Materials Lab Report Essays

1597 Words Jun 11th, 2012 7 Pages
MECH3362: Materials II
Laboratory Report

Brittle Rupture of Glass Plates

Guirguis Rezk SID 199991603 Objectives:
  To understand mechanisms of the fracture of brittle materials (in this case, glass) To recognize the variations in deformation and failure mechanisms which occur with a difference in flaw size, (i.e. between scratched and unscratched samples) Defining flaw sizes in glass plates by employing linear elastic fracture mechanics (LEFM) Utilizing the Weibull statistics approach in predicting probable failure in brittle materials.

 

Testing Procedure:
1. The thickness (t) and width (w) of the rectangular glass sample is measured. The first glass slide is placed in the Instron 3-point bending apparatus with the
Unscratched Specimens Flexural Young’s Strength Modulus
(MPa) (GPa)

1 2 3 4 5 6 7 8 9 10 Average Literature Data

62.346 41.296 58.619 58.669 53.290 47.873 54.121 47.286 39.461 44.135 50.710

76.405 58.673 71.955 76.194 70.149 59.470 74.342 71.106 62.127 68.162 68.858

103.659 98.652 96.049 124.128 73.498 83.305 78.577 91.786 93.943 131.572 97.157

80.773 84.559 90.956 86.470 80.856 82.480 80.482 87.415 87.200 79.757 84.095

Young’s Modulus E = 68 – 74 GPa

Flexural Strength ������ = 48 – 50 MPa

Page 5 of 7 G Rezk SID 199991603

Calculation of Nominal Flaw Size:
Fracture stress: ���� = ���� ���� ��
Specimen No:

Nominal Flaw Size (μm) Scratched Unscratched 46.06 104.99 52.11 52.02 63.05 78.12 61.13 80.08 114.99 91.92 74.45 16.66 18.40 19.41 11.62 33.15 25.80 29.00 21.25 20.29 10.34 20.59

Kc: Fracture Toughness – Glass fracture 1/2 toughness = 0.75 MPa m C: Nominal flaw size F: Shape Factor – Surface defect, sharp corner, with tensile stress and middle of sample F=1 Nominal Flaw Size: ���� �� = �� ������
2

1 2 3 4 5 6 7 8 9 10 Average

Distribution of Flaw Size and Weibull Modulus Calculation:

Distribution of Flaw Size
1.5 1 0.5 y = 3.0703x - 13.591 Scratched 2.5 3 3.5 4 4.5 5 Unscratched Linear (Scratched) y = 2.6723x - 8.4227 Linear (Unscratched)

ln{ln[1/(1-s)]}

0 -0.5 2 -1 -1.5 -2 -2.5 -3

ln (Flaw Size)

Weibull Modulus for Unscratched = 2.6723 Weibull Modulus for Scratched = 3.0703

Page 6 of 7 G Rezk SID

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